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Common Equity (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Schedule of Common Equity [Line Items]  
Shares available for issuance under the OIP, Shareowner Direct Plan and 401(k) Savings Plan 6,900,000
Ownership percentage 15.00%
Initial right entitlement, number of shares of common stock shareholders have the option to purchase (in shares) 0.5
Exercise price, rights (in dollars per share) 110
Percentage of exercise price upon change in beneficial ownership 200.00%
IPL [Member]
 
Schedule of Common Equity [Line Items]  
Common equity ratio, computation of ratio average, number of months 13 months
Common equity ratio 42.00%
Retained earnings free of dividend restrictions $ 494
WPL [Member]
 
Schedule of Common Equity [Line Items]  
Common equity ratio, computation of ratio average, number of months 13 months
Common equity ratio 51.03%
Retained earnings free of dividend restrictions $ 119
Minimum [Member]
 
Schedule of Common Equity [Line Items]  
Ownership percentage 10.00%